Secondary coating line

ABSTRACT

A secondary coating line for producing a secondary-coated optical fibre or bundle of fibres, the line including a feeding apparatus with a feed roll for feeding an optical fibre or bundle of fibres; an extruder for extruding an oversize secondary jacket around the fibre or bundle of fibres; a cooling apparatus for cooling the extruded secondary jacket, the distance between the extruder and the point where the cooling apparatus starts to cool being adjustable; and a winding apparatus for winding the finished secondary-coated fibre or bundle of fibres on a take-up roll. To maintain the high quality of the final product even as the line speed changes, the secondary coating line of the invention further including means for determining the point where the cooling apparatus starts to cool, means for determining the speed of the finished secondary-coated fibre or bundle of fibres, and means for adjusting the point where the cooling apparatus starts to cool in accordance with the speed of the finished secondary-coating fibre or bundle of fibres.

BACKGROUND

The invention relates to a secondary coating line for producing asecondary-coated optical fibre or bundle of fibres, the line comprisinga feeding apparatus with a feed roll for feeding an optical fibre orbundle of fibres; an extruder for extruding an oversize secondary jacketaround the fibre or bundle of fibres; a cooling apparatus for coolingthe extruded secondary jacket, the distance between the extruder and thepoint where the cooling apparatus starts to cool being adjustable; and awinding apparatus for winding the finished secondary-coated fibre orbundle of fibres on a take-up roll.

A conventional secondary coating line with the basic structure describedabove is known e.g. from Finnish Patent 75,939, or corresponding BritishPatent Application 2,141,557. Conventionally, secondary coating lineslike this have been controlled so that a product produced during thestarting and speeding up of the line has not met the qualityrequirements. The reason for this is that when the speed of the linechanges, the characteristics of the produced secondary coating alsochange; not until the normal running speed is achieved does thesecondary coating reach the desired values. A rather large amount ofvaluable optical fibre has thus been wasted.

Alternatively, optical fibres have not been thread into the tubeprovided by the secondary jacket until the production speed has beenachieved. Plastic waste has been produced, and the production speed musthave been adjusted to be so slow that it has been possible to thread theoptical fibres into the secondary jacket at that rate.

When optical fibres are thread into the secondary jacket at a rate thatis slower than the normal running speed, the poor quality of the productis at least primarily due to the fact that the distance between thecooling apparatus and the extruders has not been suitable consideringthe rate. In practice, the plastic melt outlet from the press head formsafter the press head a conical part in which the secondary jacket tubeis drawn to its final measurements. If the water cooling conducted inthe cooling apparatus is started at the conical part, the result is abrittle tube, i.e. the tensile strength of the tube in a tension test issmall. If on the other hand the distance between the press head and thewater cooling is too long, the hot plastic may run, causing faults inshape and variation in diameter. As the line speed increases, thetension cone following the press head becomes larger; by suitablyadjusting the line speed, it has thus been possible to make themeasurements of the secondary jacket comply with the qualityrequirements.

In secondary coating, the type of plastic from which a secondary jacketis produced must also be taken into account. Since different plastictypes have different characteristics, they behave differently in anextruder, and so the plastic melt also behaves differently and the linespeed must be suitable in order that it might be possible to achieve thedesired measurements.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a new kind ofsecondary coating line by which the quality of the secondary-coatedoptical fibre or bundle of fibres can be maintained high irrespective ofthe plastic type used, the line speed, or possible controlled changes inthe line speed during the production process. This is achieved with thesecondary coating line of the present invention, which is characterizedby comprising means for determining the point where the coolingapparatus starts to cool, means for determining the speed of thefinished secondary-coated fibre or bundle of fibres, and means foradjusting the point where the cooling apparatus starts to cool inaccordance with the speed of the finished secondary-coated fibre orbundle of fibres.

Thus the basic idea of the present invention is that if the point wherethe cooling is started is adjusted in accordance with the line speed,the final product always meets the quality requirements, irrespective ofthe line speed. Advantageously, the means for adjusting the point wherethe cooling apparatus starts to cool comprise a first memory means forstoring product-specific secondary jacket data about the desired pointfor starting the cooling operation of the cooling apparatus at variousspeeds of the finished secondary-coated fibre or bundle of fibres. Onthe basis of the information obtained during the trial runs, it ispossible to determine the conditions--which are dependent on the plastictype used and the desired measurements of the final product--under whicha product with the desired characteristics is obtained. Accordingly, onthe basis of the product specifications, it is thus possible todetermine the point where the cooling is to be started, when the linespeed is known.

In order that all the possible factors affecting the quality of theproduct might be controlled, the secondary coating line of the inventionadvantageously also comprises a second memory means for storingproduct-specific secondary jacket data about the throughput of theextruder at different rotation rates of the pressing screw of theextruder, and means for adjusting the rotation rate of the pressingscrew of the extruder to produce the desired throughput at variousspeeds of the finished secondary-coated fibre or bundle of fibres. Thismakes it possible to take into account any non-linearities of theoperation of the extruder and to eliminate their effect.

In accordance with the above, the secondary coating line of theinvention makes it possible to reduce and increase the line speedwithout impairing the quality of the product. For optimal utilization ofthis characteristic, the line further comprises means for determiningthe length of a finished secondary-coated fibre or bundle of fibreswound on a take-up roll, and means for decelerating the speed of afinished secondary-coated fibre or bundle of fibres to a roll changespeed as the desired length has been wound, and for accelerating it backto the normal speed after the change of rolls.

In the following, the secondary coating line of the invention will bedescribed in greater detail with reference to the attached drawing,which shows a schematic general view of a secondary coating lineaccording to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The figure shows a secondary coating line according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

For the sake of clarity, only those elements of the secondary coatingline that are significant to the operation are shown in the figure. Forexample, elements conventionally contained in secondary coating linessuch as a tension apparatus for directing a desired tensile force to thesecondary jacket, or an apparatus connected with the extruder forfeeding grease through the extruder into the secondary jacket so that itfills the jacket, or different measuring devices for measuring e.g. thediameter of the product are not depicted. Conventional line elements ofthis kind are disclosed e.g. in above-mentioned Finnish Patent 75,939and corresponding British Patent Application 2,141,557.

Basically, a secondary coating line according to the invention as shownin the figure comprises a feeding apparatus with a feed roll 1 forfeeding an optical fibre or bundle of fibres 2, an extruder 3 forextruding an oversize secondary coating around the fibre or bundle offibres 2, a cooling apparatus 4 for cooling the extruded secondaryjacket, and a winding apparatus 5 for winding the finishedsecondary-coated fibre or bundle of fibres 6 on a take-up roll 7. Asshown in the figure, the secondary coating line according to theinvention further comprises a control computer 10 that contains storageareas and processors for performing different tasks. The controlcomputer 10 comprises a storage area 11, in which the points where thecooling apparatus 4 starts to cool at various line speeds are stored. Ablock 15 of the control computer 10 obtains the data indicating the linespeed e.g. from a wheel 9 connected with the winding apparatus 5.Naturally, all conventional arrangements for measuring the line speedare suited for the purpose. On the basis of the measured line speed andthe `recipe-specific` data in the storage area 11, an actuator 8 of thecontrol computer 10 controls the cooling chute 17 that is connected withthe cooling apparatus 4 and has e.g. a telescopic structure, so that thedistance between the cooling chute 17 and the extruder 3 is as desired.The cooling conditions of the secondary jacket can thus be held constant30 irrespective of the length of the tension cone of the extrudedsecondary jacket, the length in turn depending on the desiredmeasurements of the final product, the material of the secondary jacket,and the line speed.

To control the position of the telescopic part 17 of the cooling chute,the control computer 10 naturally also needs information about thecurrent position of the telescopic part, i.e. the point where thecooling is started. The control computer 10 obtains this information byconventional sensors in connection with the actuator 8. On the basis ofboth the point where the cooling is started and the line speed, andusing the data stored in the memory means 11 concerning theproduct-specific point of the secondary jacket where the coolingoperation of the cooling apparatus is to be started at various linespeeds, the control computer 10 is able to give the actuator 8 a signalthat moves the telescopic part 17 to the desired direction. Since theactuator 8 performs a continuous sensing operation, the control computeris continuously informed of the position of the telescopic part, and sothe control computer can continuously modify the position of thetelescopic part in accordance with the line speed. The modification canbe performed so quickly that it is possible to start the line at a verylow speed and even at this speed to meet the quality requirements set tothe product, and further to accelerate the line until it reaches thedesired speed without impairing the quality of the product.

In the secondary coating line of the invention, it is also possible totake into account that the operation of the extruder may be non-linear.Accordingly, the control computer 10 comprises a second storage area ormemory means 12 for storing the product-specific secondary coating dataabout the throughput of the extruder at different rotation rates of thepressing screw of the extruder. In order that the throughput of theextruder 3 might be made to comply with the varying line speeds, thecontrol computer 10 comprises suitable software which--after receivingdata about the line speed--gives the actuator 13 that adjusts therotation rate of the pressing screw of the extruder a control signalthat product-specifically sets the rotation rate of this pressing screwto the desired value at the various line speeds. This rectification ofpossible non-linearities of the extruder further enhances the operationof the line especially in situations where the line speed varies withina relatively large range.

The characteristic of the secondary coating line according to theinvention--that the line is able to produce a final product that meetsthe quality requirements irrespective of the line speed--is also.advantageous with respect to continuous operation: instead of aconventional double winder, the line can now be provided with a muchcheaper single winder, since the change of rolls does not require thatthe line should be stopped. Accordingly, the winding apparatus 5 of thedescribed line has an actuator 14, typically a separate production lineactuator, measuring the length of the final product of the secondarycoating line wound on the take-up roll 7. The data indicating the woundlength is sent to a block 16 of the control computer; by a programcontained in the block and by utilizing other storage areas andprocessors of the computer 10, the speed of the secondary coating linecan be decelerated to a roll change speed as the desired length has beenwound, and accelerated back to the normal speed after the change ofrolls. According to the invention, when the length of the product woundon the take-up roll reaches the desired value, block 16 of the controlcomputer 10 can, if desired, slow the line speed down to a point wherethe take-up roll 7 can be changed in a single winder even without anaccumulator. When the take-up roll has been changed, block 16controlledly accelerates the line speed back to the normal runningspeed; the production process has not been interrupted, nor has thequality of the product been impaired in any way by the change of rollsor associated changes in the speed.

The secondary coating line of the invention has been described above bymeans of one illustrative and schematic solution, but it is to beunderstood that the line can be modified in many ways according to theneed and that additional elements can be added without departing fromthe scope of the attached claims.

I claim:
 1. A secondary coating line for producing a secondary-coatedoptical fibre or bundle of fibres, the line comprising:a feedingapparatus with a feed roll for feeding an optical fibre or bundle offibres, an extruder for extruding an oversize secondary coating aroundthe fibre or bundle of fibres, a cooling apparatus for cooling theextruded secondary coating, the distance between the extruder and thepoint where the cooling apparatus starts to cool being adjustable; awinding apparatus for winding the finished secondary-coated fibre orbundle of fibres on a take-up roller; means for determining the pointwhere the cooling apparatus starts to cool; means for determining thespeed of the finished secondary-coated fibre or bundle of fibres; andmeans for initially setting and subsequently adjusting the positionwhere the cooling apparatus starts to cool in accordance with the speedof the finished secondary-coated fibre or bundle of fibres, said meanscomprising a first memory means for storing product-specific secondarycoating data including points for starting the cooling operation of thecooling apparatus at various speeds of specific finishedsecondary-coated fibres or bundles of fibers, said data determining theinitial position of the cooling apparatus.
 2. A secondary coating lineaccording to claim 1 and further comprising a second memory means forstoring product-specific secondary jacket data including extruderthroughput at different rotation rates of the pressing screw of theextruder, andmeans for adjusting the rotation rate of the pressing screwof the extruder to produce the desired throughput at various speeds ofthe finished secondary-coated fibre or bundle of fibres.
 3. A secondarycoating line according to claim 1 and further comprisingmeans fordetermining the length of a finished secondary-coated fibre or bundle offibres wound on a take-up roll, and means for decelerating the speed ofa finished secondary-coated fibre or bundle of fibres to a roll changespeed as the desired length has been wound, and for accelerating it backto the normal speed after the change of rolls.